Handling of Terminating Calls in a Distributed System

ABSTRACT

A technique for handling mobile terminating calls in a distributed switch is described. The switch includes at least one cluster wherein the at least one cluster comprises a plurality of cluster members. Each cluster member is associated with a set of roaming numbers and adapted to route a mobile terminating call to either a recipient subscriber served by the cluster member or to another cluster member which serves the recipient subscriber. The at least one cluster further comprises a first data structure having a content that is common to and accessible by all the cluster members of the cluster. The first data structure specifies the plurality of cluster members and the roaming number set associated with each cluster member.

FIELD OF THE INVENTION

The invention generally relates to call routing techniques in mobiletelecommunication networks. In particular, the invention relates to atechnique for routing a mobile terminating call or a handover call to aterminating switch where the recipient subscriber of the call is locatedin the network.

BACKGROUND OF THE INVENTION

Call routing in a mobile telecommunication network is different from andgenerally more complicated than that in a fixed telecommunicationnetwork. In a fixed network such as a Public Switched Telephone Network(PSTN), a user terminal is permanently connected to a central office, ora central switch. In a mobile telecommunication network on the otherhand, a subscriber can roam freely from the service area of one switchto that of another. That is to say, the switch which serves the mobilesubscriber—providing switching functions including call routing—maychange from time to time.

From the perspective of a calling party who wishes to place a call to amobile recipient subscriber, a change in the serving switch of therecipient subscriber is invisible. Whether the recipient subscriber islocated within the service area of his “home” switch, i.e. the switch atwhich he registers with the mobile communication network, or is underthe service of a different switch, the calling party always dials oneand the same telephone number, or directory number, of the recipientsubscriber. This number is usually called the Mobile Subscriber ISDN(MSISDN) of the recipient subscriber.

In order to route the call to the recipient subscriber, the switchingsystem of the mobile network internally assigns a number that isdifferent from the MSISDN, a so-called roaming number, to the call anduses this roaming number to determine how to route the call to theterminating switch of the call, that is, to the particular switch whichserves the recipient subscriber at the time of the call. The roamingnumber is often called the Mobile Station Roaming Number (MSRN). MSRNsare related to the geographical numbering plan, and they are notassigned to nor visible to any subscriber. In summary, by means of theMSRN number associated with a mobile terminating call, the switchingsystem of the mobile communication network can route the call to theterminating switch serving the recipient subscriber of the call. Asimilar mechanism is used for handovers.

With the development of distributed computing, more and more switches inmobile telecommunication networks are being implemented as distributedsystems, also called switch clusters. In the language of distributedcomputing, a “cluster” is a set of loosely coupled computing devicesthat work together closely so that in many aspects they can be viewed asthough they are a single computing device. A cluster usually contains anumber of cluster members, or blades. A cluster member is a computingdevice having all the essential functional components to be consideredas a computer while lacking certain features of a stand-alone device forthe consideration of space, power, etc.

Applying the cluster paradigm, each switch can be configured as a switchcluster having a plurality of cluster members. That is, a service areawhich used to be served by one stand-alone switch can now be served by ahighly compact switch cluster. The cluster approach provides thebenefits of load balancing and high availability, to name a few. Forinstance, in order to keep the load for each cluster member as even aspossible, a distribution mechanism distributes all subscribers served bythe service area of the switch cluster over all cluster members.

In principle, each cluster member can perform the switchingfunctionalities just as a conventional stand-alone switch does. Forexample, each cluster member can handle mobile originating traffic, canreceive an incoming call, can route the incoming call to the switchcluster who currently serves the recipient subscriber of the call, andcan terminate the incoming call if the recipient subscriber is served bythe cluster member itself. Thus, in a distributed switching system withone or more switch clusters wherein each cluster owns a plurality ofcluster members, it is necessary for the switching system to determine,for each incoming mobile terminating call, not only the terminatingswitch cluster but also the very cluster member (in the terminatingswitch cluster) who serves the recipient subscriber of the call.

Accordingly, there is a need for a technique to efficiently handlemobile terminating calls, and handover calls, in a distributed switchingsystem.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a switch for a mobilecommunication network is provided. The switch includes at least onecluster, and the at least one cluster comprises a plurality of clustermembers, or blades. Each cluster member is associated with, or “owns”, aset of numbers. Further, each cluster member is adapted to either routean incoming call to a recipient subscriber served by the cluster memberitself—in other words, to “terminate the call”—or to route the call toanother cluster member in the cluster (or, optionally, to a network nodeoutside the cluster); the call routing is based on a number associatedwith the incoming call. The at least one cluster of the switch furthercomprises a first data structure which specifies the plurality of thecluster members in the cluster and the number set that is associatedwith each cluster member. The content of this first data structure isshared by all the cluster members, that is, it is common to all thecluster members and all the cluster members have access to it.

Effectively, all the number sets associated with all the cluster membersmay be contained in the first data structure. The first data structuremay contain further information, such as information specifying arouting address for each cluster member, or for each number setassociated with the cluster member. This cluster member routing addressmay be used by the cluster member receiving the incoming call to routethe call either to the recipient subscriber served by the clustermembers or to another cluster member. The cluster member routing addressmay take various formats. One choice of format is the Internet Protocol(IP) address format. Any other conventional address format, such as apoint code, is equally applicable.

The switch may further comprise a second data structure. The second datastructure defines, with respect to each of the plurality of number setsassociated with the cluster members, whether the call routing should behandled within the cluster or by a network node outside the cluster. Anetwork node outside the cluster may be another cluster within the sameswitch, another switch within the same mobile communication network, oreven a cluster or a switch in another network. The network node is notlimited to clusters or switches alone; it may be any network node thatis equipped with number analysis and call routing functionalities.

The two data structures may be associated, or linked, with each other.There are many ways to create such an association. As one example, thetwo data structures may be implemented as two tables in a relationaldatabase wherein the two tables are linked with each other by the numbersets (since the plurality of number sets are defined in both the firstand the second data structure). Another implementation is to merge theinformation of the two tables into one table. Other implementationsknown in the art are also possible. The content of the second datastructure may be common to all the cluster members in the cluster, andall the cluster members may be provided with access the content.

The first data structure may be stored in a central database of thecluster accessible by each cluster member. Likewise, the second datastructure may also be stored in the central database of the cluster.Furthermore, each cluster member may comprise a local copy of at leastone of the first and second data structure.

The number associated with the call and used for routing purposes may bea roaming number, for example an MSRN. The number could also be aHandover Number (HON). To minimize administrative efforts, consecutiveMSRNs or HONs may be grouped into a series, and one or more MSRN or HONseries may be comprised in a number set associated with one clustermember. Of course, the requirement of consecutive numbers in the numberset is not a must. In the MSRN or HON scenario, the first data structuremay define the owning cluster member of each MSRN or HON number set, andthe second data structure may be a routing table for routing incomingcalls associated with MSRNs or HONs.

According to another aspect of the invention, a method for handling callrouting in a mobile communication network is provided. The mobilecommunication network comprises a switch including at least one cluster,and the cluster comprises a plurality of cluster members. Each clustermember is associated with a set of numbers and is adapted to route anincoming call to either a recipient subscriber served by the clustermember or to another cluster member. The call routing is handledaccording to a number associated with the incoming call. The callrouting method of the invention comprises the following steps: a firstcluster member is provided with access to a content of a first datastructure which specifies the plurality of cluster members of thecluster and the number set associated with each cluster member, thecontent of this first data structure being common to and accessible byall the cluster members in the cluster; the first cluster memberreceives an incoming call; then, the first cluster member determines,based on the number associated with the call and based on the content ofthe first data structure, the particular cluster member which currentlyserves the recipient subscriber of the call.

The method may further comprise routing the call according to the resultof the above determination. That is, if it is determined that the firstcluster member is the particular cluster member serving the recipientsubscriber of the call, the call is routed to the subscriber, or“terminated” at the first cluster member. If it is determined that therecipient subscriber is served by another cluster member, the call isthen routed to the other cluster member.

As described above, the first data structure may further specify, withrespect to each number set or each cluster member, an associated clustermember routing address. In this case, dependent on the result of theabove determination, the first cluster member can determine the routingaddress via which the call can be further routed.

For example, when it is determined that it is a second cluster memberwho serves the recipient subscriber, the routing address of the secondcluster member will be obtained from the content of the first datastructure, and the call will be routed to the second cluster member viathe corresponding routing address.

As mentioned above, the switch according to the invention may comprise asecond data structure which defines, with respect to each of theplurality of number sets associated with all the cluster members,whether the call routing should be handled within the cluster or by anetwork node outside the cluster. Correspondingly, the method of theinvention may further comprise the following steps: the first clustermember, which receives the incoming call, is provided with access to acontent of the second data structure; the first cluster member thendetermines, based on the number associated with the call and theinformation contained in the second data structure, whether the callshould be handled within the cluster or by a network node outside thecluster; and, if it is determined that the call should be handled by anetwork node outside the cluster, the first cluster member then routesthe call to that network node.

According to a further aspect of the invention, a computer programproduct is provided. The computer program product comprises program codeportions for performing the steps of the method of the invention whenthe computer program product is executed on a switch or a component of aswitch. The invention can be practised by means of hardware, software,or a combined hardware/software approach. As for a software aspect, thecomputer program product may be stored on a computer-readable recordingmedium.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention will be described with reference to exemplaryembodiments illustrated in the drawings, wherein:

FIG. 1 shows a schematic block diagram illustrating the procedure of HLRinterrogation in a conventional switching system;

FIG. 2A shows a schematic block diagram illustrating an embodiment ofthe switch of the present invention;

FIG. 2B shows a schematic block diagram illustrating another embodimentof the switch of the present invention;

FIG. 3 shows a flow chart illustrating a method embodiment of thepresent invention;

FIG. 4 shows two tables illustrating two respective embodiments of thefirst data structure of the present invention;

FIG. 5 shows two tables illustrating an embodiment of the first datastructure and the second data structure of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates the procedure of Home Location Register (HLR)interrogation in a conventional switching system 100. The basic HLRinterrogation procedure shown in FIG. 1 is used in all conventionalmobile communication networks for national and international roaming. Asimilar procedure is used for handovers, wherein the HON is used toroute the call to a non-terminating switch. In some implementations theMSRNs can at the same time be used as HONs.

As shown in FIG. 1, the switching system 100 comprises a Gateway MobileSwitching Center (GMSC) 102 through which a mobile terminating callarrives, as indicated by arrow 104. The incoming call is associated withan MSISDN number which has been dialed by the calling party. A GMSC isbasically a switch capable of interrogating the subscriber's HLR toobtain routing information, and thus contains a table linking an MSISDNto the corresponding HLR. Although the GMSC function is distinct from anormal Mobile Switching Center (MSC) function, it is usually implementedin an MSC. In the case of a switch cluster, the GMSC function istypically implemented in a cluster member.

The switching system 100 further comprises an HLR 106 which stores theVisitor Location Register (VLR) addresses of terminating nodes. Aterminating node is the network node which serves the recipientsubscriber of the call. In FIG. 1, this terminating node is an MSC 108.The most general call routing procedure begins with GMSC 102 queryingthe called subscriber's HLR 106 for an MSRN. Upon receiving the call,GMSC 102 forwards the MSISDN number to HLR 106, as shown by arrow 110.In the HLR 106, the MSISDN number is used to obtain the InternationalMobile Subscriber Identity (IMSI) of the recipient subscriber as well asthe VLR address of the terminating MSC 108. Next, the IMSI is forwardedto the terminating MSC 108, as shown by arrow 112.

At MSC 108, by means of the IMSI, a temporary roaming number, i.e. MSRN,is assigned to the call. MSC 108 owns a pool, or a set, of MSRNs.Thereafter, the assigned MSRN is returned to GMSC 102 via HLR 106, asshown by arrows 114 and 116, respectively. Finally, GMSC 102 uses theMSRN to route the call to MSC 108.

FIGS. 2A and 2B illustrate two embodiments of switches for a mobilecommunication network. The switches may be part of the switching system100 of FIG. 1 (and incorporate, for example, one or both of GMSC 102 andMSC 108) and participate in the HLR interrogation procedure explainedabove.

Specifically, FIG. 2A shows a schematic topography of a switch 200. Theswitch 200 comprises a single switch cluster 202 serving a service area204. Of course, depending on the hardware and/or software capacity ofthe switch 200, the number of subscribers served in the service area204, and/or the volume of the network traffic within the service area204, the switch 200 may be configured to comprise multiple suchclusters.

The cluster 202 comprises a plurality of cluster members, or blades,206, 208, 210, 212 and 214. Similar as the role of multiple clusters ina switch, multiple cluster members in a cluster provide a further levelof load balancing and increased availability. The basic configurationand the functionality of one cluster member is the same as that ofanother. As shown in FIG. 2A, each cluster member 206, 208, . . . , 214is associated with a number set 216, 218, . . . , 224, respectively.Each number set, 216 for example, contains roaming numbers such asMSRNs. At HLR interrogation, one MSRN from a certain number set isassigned to the incoming call. As to be explained below, the assignedMSRN number will be used by the cluster 200 to determine how the callwill be routed.

Although not absolutely necessary, it is preferable that each number setcontains a series of consecutive numbers in association with therespective cluster member. An example of a series of MSRNs is shown inFIG. 2A for the number set 216: 49172999991, 49172999992, 49172999993,49172999994, and 49172999995. In principle, multiple such MSRN seriesmay be included in the number set 216. The number set associated with acluster member may be dynamic; that is to say, existing MSRNs or MSRNseries in the number set 216 may be deleted or changed, and/or new MSRNsor MSRN series may be added into the number set 216. A dynamic numberset is useful for the administration of the entire switch 200 in view ofthe increase or decrease of the number of subscribers in the servicearea, increase or decrease in the network traffic, and/or the capacityof the cluster or the cluster members.

The cluster 202 further comprises at least one first data structure 225.The first data structure 225 specifies for the cluster 202 the pluralityof cluster members 206, 208, 210, 212, and 214 thereof and the numberset associated with each cluster member. More details about the firstdata structure are to provided in the description of FIG. 4 below.

As FIG. 2A indicates, the first data structure 225 is stored in acentral database 227 of the cluster 202. The central database 227 isaccessible by each cluster member. Naturally, as can be understood bythose skilled in the art, one or more backup copies or mirror copies ofthe first data structure 225 may be provided in the cluster for thebenefit of better performance and/or increased availability.

Alternatively, each cluster member may store or comprise a local copy ofthe first data structure 225. This case is shown in FIG. 2B, wherein thecluster members 206, 208, and so on each comprise a local copy of thefirst data structure 225. The provision of local copies is beneficialfor a fast and reliable performance of the cluster members 206, 208,210, 212, and 214.

As figuratively depicted in the two embodiments of FIGS. 2A and 2B, thefirst data structure 225 (and its content) is in each case common to andaccessible by each of the plurality of cluster members 206, 208, 210,212, and 214. The provision of a common version of the first datastructure is advantageous as it facilitates the administration andmaintenance of the content of the first data structure (which can becomequite voluminous). In other words, it is not necessary to provide eachof the cluster members 206, 208, 210, 212, and 214 with an individualversion of such a data structure. Rather, a common version of the firstdata structure 225 is either provided in a centralized manner (FIG. 2A)or in a distributed manner (FIG. 2B) such that the common version is ineach case accessible by the various members 206, 208, 210, 212, and 214of the cluster 202. Accordingly, the first data structure 225 can beadministered and maintained centrally and then be loaded either into thecentral database 227 as shown in FIG. 2A or into the local databases asshown in FIG. 2B. Of course, the embodiments of FIGS. 2A and 2B could becombined in such a manner that the data structure 225 is downloaded fromthe central database 227 of FIG. 2A to the local databases of FIG. 2B.

Next, an embodiment of a call routing method 300 for a mobilecommunication network will be described in detail with reference to FIG.3. In order to provide a more thorough understanding, the method 300will exemplarily be described in relation to the switch 200 of FIGS. 2Aand 2B. It should be noted that the method 300 could also be practicedin combination with switches that have a different configuration.

The method 300 begins with providing, at step 302, a first clustermember 206 with access to the first data structure 225, the content ofwhich is common to and accessible by all the cluster members. The firstcluster member 206 receives, at a next step 304, an incoming callassociated with an MSRN which has been assigned to the call during theHLR interrogation.

The first cluster member 206 may not be the cluster member which servesthe recipient subscriber of the call. Thus, at a next step 306, thefirst cluster member 206 determines the particular cluster memberserving the recipient subscriber. The determination is performed basedon the MSRN associated with the call and the information contained inthe first data structure 225. For instance, the first cluster member 206examines the MSRN associated with the call, determines the number setwhich includes this MSRN, looks the number set up in the content of thefirst data structure 225, and finds the cluster member that isassociated with the number set. As mentioned earlier, since the numbersin a number set are preferably in a consecutive order, the first clustermember 206 can efficiently determine to which number set the MSRNassociated with the call belongs.

After the first cluster member 206 has determined the serving clustermember of the recipient subscriber, the first cluster member 206 mayfurther route the call, depending on the result of the determination, toeither the recipient subscriber or to a second cluster member, 208 forexample. In particular, if it has been determined that the first clustermember is the very cluster member which serves the recipient subscriber,the call is then routed to the subscriber. If, on the other hand, it hasbeen determined that a second cluster member 208 is the serving clustermember, the call is then routed to the second cluster member 208 via aconnection existent between the two cluster members.

As will be described below, the first data structure may furtherspecify, with respect to each number set or each cluster membercontained therein, an associated cluster member routing address. Thus,once the particular cluster member serving the recipient subscriber isdetermined, the method 300 may continue with the following furthersteps: the first cluster member 206, knowing the second cluster member208 is the serving cluster member, can determine the routing address ofthe second cluster member 208 by looking it up in the first datastructure; consequently, the first cluster member 206 can route the callto the second cluster member 208 via the determined routing address.

The method 300 may comprise additional steps. The first cluster member206 may be provided with access to the content of a second datastructure (more details will be provided in the description of FIG. 5below). In a nutshell, the second data structure defines, with respectto each of a plurality of number sets associated with all the clustermembers in the cluster 202, whether the call routing should be handledinside the cluster 202 or outside. By accessing the second datastructure (i.e. its content), the first cluster member 206 candetermine, based on the MSRN number associated with the incoming call,whether the call should be handled by a cluster member or a network nodeoutside the cluster 202. If it is determined that the call routingshould handled by a network node outside the cluster 202, the firstcluster member 206 routes the call to that network node accordingly;otherwise, the first cluster member 206 handles the call routing itself.

Preferably, the above additional steps are performed after the firstcluster member 206 receives the incoming call, at step 304, and beforethe first cluster member 206 determines the particular cluster memberserving the recipient subscriber, at step 306. In this case, the callrouting method 300 is a two-phase procedure. In the first phase, thecluster member receiving the incoming call determines whether the callshould be handled inside or outside the cluster; if it is decided thatthe call should be handled within the cluster, the receiving clustermember continues with the second phase to determine which cluster memberwithin the cluster is serving the recipient subscriber. If the receivingcluster member is actually the serving cluster member of the recipientsubscriber, the call is straightforwardly routed to the subscriber; ifit is another cluster member within the cluster who is serving therecipient subscriber, the receiving cluster member then routes the callto this serving cluster member.

In FIG. 4, two tables are shown to illustrate two embodiments of thefirst data structure 225. The upper table shows the basic configurationof the first data structure 225. In this basic configuration, two lists(or columns, or groups) of information are presented. The first list, onthe left hand side, is a list of the MSRN number sets (each containing,for example, 10 consecutive MSRNs) associated with the cluster membersin the cluster. The second list, on the right hand side, is a list ofcluster members, each with an individual identifier 1, 2, 3, and so on.Of course, the identifier may take any format known in the art. As shownin the table, each of the listed MSRN sets is associated with aparticular cluster member (namely the member being in the same line ofthe data structure 225 as the particular MSRN set, thus the MSRN set49172999991 and cluster member 1 are associated with each other, and soon). By using such a configuration, the first data structure 225 definesall the cluster members within the cluster and the MSRN number setsassociated with them. By accessing the information in the first datastructure 225, a cluster member is able to determine, based on the MSRNassociated with an incoming call, the cluster member who “owns” thecorresponding MSRN number set, i.e. the particular cluster member whoserves the recipient subscriber of the call.

The lower table in FIG. 4 shows an extended configuration 225′ of thefirst data structure 225. As can be easily seen, the extended first datastructure 225 additionally contains a third list, a list of IP routingaddresses, corresponding to a MSRN number set and a correspondingcluster member. With the routing address information included in thefirst data structure 225, the cluster member who receives the call mayfurther route the call to the serving cluster member of the recipientsubscriber via the determined routing address (or terminate the calllocally if required). In the version shown in FIG. 4, the MSRN set49172999991 and cluster member 1 are associated with the IP address192.168.52.1, and so on.

In FIG. 5, the upper table represents the first data structure 225, andthe lower table illustrates an embodiment of a second data structure 240associated with the first data structure 225. The content of the seconddata structure 240 is common to and accessible by all the clustermembers of the cluster. The second data structure 240 may, for example,be stored in the central cluster database 227 (FIG. 2A) or locally ateach cluster member (FIG. 2B).

The second data structure 240 is an MSRN routing table which defines howa mobile terminating call should be routed based on an analysis of theMSRN number associated with the call. The MSRN routing table is alsoknown as the B-number analysis table. As shown in the MSRN routing tableof FIG. 5, for each MSRN number set, a route is indicated: a callassociated with an MSRN number belonging to one of the number sets49172999991, −2 and −3 should be handled inside the cluster; a call withan MSRN number falling in the number set of 49173002 should be handledby a network node outside the cluster and so on. In summary, the seconddata structure 240 determines whether an incoming call should be handledwithin the cluster or by a network node outside the cluster.

When it is determined, based on the content of the second data structure240, that an incoming call should be handled within the cluster, thenthe first data structure 225 is consulted to identify the particularcluster member that is to terminate the call (as indicated by the arrow400). Since both the first data structure 225 and the second datastructure 240 include a list of all the MSRN number sets owned by acluster, the two data structures are associated, or linked, with eachother by means of these number sets.

Although embodiments of the present invention have been illustrated inthe accompanying drawings and described in the foregoing description, itshould be understood that the invention is not limited to theembodiments disclosed herein. In particular, the invention can also bepracticed in (non-terminating) handover scenarios based on a HON that isassigned to a call. Moreover, the invention is capable of numerousrearrangements, modifications, and substitutions without departing fromthe spirit and scope of the invention as set forth and defined by thefollowing claims.

1. A switch for call routing in a mobile communication network, theswitch including a cluster, the cluster comprising: a plurality ofcluster members, each cluster member being arranged to terminate anincoming call to a recipient subscriber service by the cluster member orto route the incoming call to another cluster member, wherein a numberis associated with each incoming call, the associated number comprisingat least one of a Mobile Subscriber Router Number (MSRN) and a HandoverNumber (HON), each cluster member having a set of numbers associatedtherewith, each of the numbers of the set of numbes comprising at leastone of an MSRN and HON, and incoming calls associated with a number fromthe set of numbers being terminated at the associated cluster member; acomponent arranged to provide a first data structure common to andaccessible by, all the cluster members, wherein the first data structurespecifieds each of the cluster members and the number set associatedwith each of the cluster members; a component arranged to receive anincoming call by one of the cluster members; and a component arranged todetermine, by the receiving cluster member, the particular clustermember to terminate the incoming call by consulting the first datastructure based on the number associated with the received call.
 2. Theswitch of claim 1, wherein the first data structure further specifies,with respect to each number set or each cluster member, an associatedcluster member routing address.
 3. The switch of claim 2, wherein therouting address is an Internet Protocol address.
 4. The switch of claim1, further comprising a second data structure defining, with respect toeach of a plurality of number sets, whether the call routing should behandled within the cluster or by a network node outside the cluster. 5.The switch of claim 4, wherein the second data structure is associatedwith the first data structure.
 6. The switch of claim 4, wherein acontent of the second data structure is common to and accessible by thecluster members.
 7. The switch of claim 1, wherein at least one of thefirst and second data structures structure is stored in a centralcluster database that is accessible by each cluster member.
 8. Theswitch of claim 1, wherein each cluster member comprises and accesses alocal copy of at least one of the first and second data structure. 9.(canceled)
 10. A call routing method for a mobile communication networkcomprising a switch including at least one cluster, the clustercomprising; a plurality of cluster members, each cluster member beingarranged to terminate an incoming call to another cluster member,wherein a number is associated with an incoming call to a recipientsubscriber served by the cluster member or to route the incoming call toanother cluster member, wherein a number is associated with an incomingcall, the associated number comprising at least one of a MobileSubscriber Routing Number (MSRN) and a Handover Number (HON), whereineach cluster member has a set of numbers associated therewith, each ofthe numbers of the set of numbers comprising at least one of an MSRN andHON, and an incoming call associated with a number from the set ofnumbers is to be terminated at the associated cluster member; providinga first data structure common to and accessible by all the clustermembers, wherein the first data structure specifies each of the clustermembers and the number set associated with each of the cluster members;receiving an incoming call by one of the cluster members; anddetermining, by the receiving cluster member, the particular clustermember that is to terminate the incoming call by consulting the firstdata structure based on the number associated with the received call.11. The method of claim 10, further comprising the steps of: the firstdata structure further specifying, with respect to each number set oreach cluster member, an associated cluster member routing address,determining the routing address of the particular cluster memberdifferent from the receiving cluster member; and routing the call to theparticular cluster member via the determined routing address.
 12. Themethod of claim 10, further comprising the steps of: providing thereceiving cluster member with access to a content of a second datastructure defining, with respect to each of a plurality of number sets,whether the call routing should be handled within the cluster or by anetwork node outside the cluster; determining, based on the numberassociated with the call and the content of the second data structure,fi the call should be handled by a network node outside the cluster: androuting the call to the network node dependent o the result of thedetermination. 13.-15. (canceled)